JP3050239B2 - Main steam isolation valve - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a main steam isolation valve provided in a nuclear power plant, and more particularly to a main steam isolation valve for preventing vibration of a valve body.

[0002]

2. Description of the Related Art In a nuclear power plant, for example, as shown in FIG. 5, steam generated in a nuclear reactor 1 is guided to a turbine 4 via a steam header 3 by a plurality of main steam pipes 2, and
After being provided with the work, the water is condensed by the condenser 5 and is returned to the reactor 1 via the water supply pump 6 and the water supply pipe 7.

Under such a configuration, each main steam pipe 2
Are provided with first and second main steam isolation valves 8 (8a, 8b) located inside and outside the reactor containment vessel 5. These main steam isolation valves 8 close at a high speed when receiving an emergency signal such as a low reactor water level, a high main steam pipe radioactivity, a high main steam pipe ambient temperature, or a low turbine inlet pressure. Has become.

Incidentally, the main steam isolation valve 8 is, for example, shown in FIG.
As shown in FIG. 7, a valve box 14 having a cylindrical valve chamber 13 intersecting at an inclination of, for example, 45 ° is provided between a primary flow path 11 and a secondary flow path 12 arranged substantially linearly. ing. A piston-shaped valve element 15 is inserted into a valve chamber 13 of the valve box 14. The valve element 15 is supported on its outer periphery by a plurality of guide ribs 16a, 16b, 16c and is slidable over an open / close position. .

[0005] One guide rib 16a is formed of an independent member, and is disposed substantially at the center of the flow path. The other two guide ribs 16b and 16c are formed as protrusions protruding from the inner surface of the peripheral wall of the valve box 14, and are arranged, for example, 120 ° to the left and right with respect to the one guide rib 16a.

During operation of the plant, the valve element 15 is held at the valve fully open position (the position shown in FIG. 6). In this state, about half of the distal end side of the valve element 15, that is, a portion extending from the distal end to the intermediate part. Are protruding into the flow path.

[0007] In an emergency, the valve body 15 is driven by the drive mechanism 1.
7 moves to the closed position at high speed. The closed position is a position where the distal end of the valve element 15 contacts the valve seat 18 provided at the inlet of the secondary flow path 12.

The valve body 15 is provided with a valve shaft 19,
The valve shaft 19 penetrates through the valve cover 20 and is connected to the piston rod 17a of the drive mechanism 17.

[0009]

By the way, in the conventional main steam isolation valve 8, during operation of the plant, a portion from the tip to the middle of the valve body 15 projects into the flow passage and is exposed to steam. Therefore, due to the fluid force of the steam, the valve body 15
May vibrate.

Further, since the valve body 15 is formed in a cylindrical shape having a constant diameter and a bottom, the outer peripheral surface of the valve body 15 is always in contact with each of the guide ribs 16a, 16b and 16c.
Therefore, around the valve element 15, as shown in FIG. 7, the valve element 15 and the second and third guide ribs 16 are provided.
A closed space 13 a along the circumferential direction of the valve element 15 is formed by the b, 16 c and the peripheral wall of the valve box 14.

When such a closed space 13a exists, the valve element 15 exposed to the steam at the fully open position of the valve receives a fluid force in the flow direction of the steam and in the direction orthogonal to the flow.
For example, in FIG. 7, when the steam flows a and b separated from the first guide rib 16a to the left and right of the valve body 15 are blocked by the closed space 13a, there is a difference in the fluid force between the steam flows a and b. The difference acts on the valve body 15.

Since the fluid force is substantially proportional to the square of the flow rate of the steam, the fluid force becomes large enough to vibrate the valve element 15 depending on conditions such as when the flow rate is large. The reaction force directed toward the inlet of the main steam flow by this fluid is generated by the valve element 15.
Is supported only by the first guide rib 16a that supports the support, the support becomes unstable, and vibration is likely to occur.

When the valve body 15 vibrates, there is a possibility that abrasion occurs at the contact portions between the valve body 15 and the guide ribs 16a, 16b, 16c, and the reliability at the time of the valve closing operation is reduced.

The present invention has been made in view of such circumstances, and has a main steam isolation valve capable of stabilizing the support of a valve body, preventing the occurrence of vibration and wear, and improving reliability at the time of valve opening / closing operation. The purpose is to provide.

[0015]

According to the first aspect of the present invention, there is provided a valve box having a cylindrical valve chamber which intersects at a fixed inclination between a primary flow path and a secondary flow path which are arranged substantially linearly. The valve body inserted into the valve chamber of the valve box in a piston shape and a drive mechanism for driving the valve body at high speed are right. When the valve is fully opened, a portion extending from the intermediate portion to the distal end of the valve body is a flow path. In the main steam isolation valve disposed in the inside, a cylindrical holder that covers the entire outer surface of the valve body is installed at a valve body storage position of the valve chamber when the valve is fully opened, and a lower end of the holder on the flow path side is provided. Part, in the radial positional relationship of the vertical cross section with respect to the flow direction of the fluid in the flow path, an arrangement closer to the closing drive direction side of the valve in the flow path than the lower end at the fully open position of the valve. It is characterized by having done.

According to a second aspect of the present invention, in the main steam isolation valve according to the first aspect, the valve body is inserted in a piston shape with an outer periphery supported by a plurality of guide ribs in a valve chamber of the valve box.
The valve is connected to a driving mechanism that drives at a high speed, and the outer peripheral surface of at least the intermediate portion of the valve body has a smaller diameter than the outer peripheral surface of the pipe side end of the valve body, and is a small diameter portion separated from the guide rib. The space around the valve body communicates in the circumferential direction, and each of the guide ribs is exposed inward of the holder and arranged so as to be spaced apart from the outer peripheral surface of the small diameter portion of the valve body. Features.

According to the first aspect of the present invention, since the cylindrical holder that covers the entire outer surface of the valve element is installed at the valve element storing position when the valve is fully opened in the valve chamber, the valve element directly receives steam. It is no longer exposed to flow and the valve body is mechanically supported by the holder, thereby preventing vibration of the valve body. further,
By arranging the lower end of the holder on the flow path side closer to the closing drive direction side of the valve element in the flow path than the end of the valve element, it is possible to particularly effectively prevent contact with the steam flow.

According to the second aspect of the present invention, the outer peripheral surface of at least the intermediate portion of the valve body has a smaller diameter than the outer peripheral surface of the pipe-side end of the valve body and is separated from the guide ribs.
As a result, the space around the valve body is communicated in the circumferential direction, so that a closed space is not formed around the valve body unlike the related art. In addition, the guide ribs are exposed inside the holder and are disposed close to the outer peripheral surface of the small end portion of the valve body with a gap therebetween, so that steam temporarily flows into the holder and the valve body is exposed to the steam. However, the difference between the fluid forces of the steam flows separated on the left and right sides of the valve body is eliminated by the communication, and vibration of the valve body is prevented.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a main steam isolation valve according to the present invention will be described below with reference to the drawings.

As shown in FIG. 1, the main steam isolation valve of the present embodiment has a valve box 23 in which a primary flow path 21 and a secondary flow path 22 are arranged substantially linearly. Each flow path 2 of this valve box 23
A cylindrical valve chamber 24 is formed between 1 and 22. The valve chamber 24 has, for example, a 45 ° axial center on the primary flow path 22 side.
The inclination and the valve seat 24 a are formed at the inlet of the secondary flow path 22.

A piston-like valve 25 is inserted into the valve chamber 24. The valve body 25 has a cylindrical shape with a bottom end in the axial direction 25a toward the valve seat 24a, and a valve shaft 26 protrudes from the open base end 25b. Valve shaft 26
Is connected to the piston rod 29 of the drive mechanism 28 through the valve lid 27.

When the plant is in operation, the valve 25
As shown in FIG.
The valve moves to the 5b side as much as possible, and the valve is fully opened. In this state, by setting a stroke for quickly performing an emergency closing operation, about a half of the distal end side of the valve body 25, that is, a portion extending from the distal end portion 25a to the intermediate portion projects into the flow passage. ing.

In this embodiment, a cylindrical holder 30 that covers the outer surface of the valve body 25 is fixedly installed at the valve body storage position when the valve chamber 24 is fully opened. In this embodiment, the holder 30 has a length that covers the outer surface of the valve body 25 over substantially the entire axial direction. The lower end of the holder 30 in FIG. 1 is disposed below the lower end of the valve body 25, and the lower end of the holder shields the lower end of the valve body 25 from the steam flow.

The valve body 25 of this embodiment has a large diameter at both ends and a small diameter portion 25c at an intermediate portion. The outer peripheral surface of the large-diameter portion is formed by a plurality of guide ribs 31a, 31.
It is slidably supported by b and 31c. One guide rib 31a is formed by an independent member, and is disposed at a substantially central portion in the flow path. The other two guide ribs 31b and 31c are formed as ridges protruding from the inner surface of the peripheral wall of the valve box 23, and are arranged, for example, 120 ° to the left and right with respect to the one guide rib 31a. As shown in FIG. 2, each of the guide ribs 31a, 31b, 31c
The small diameter portion 25c protrudes into the inside of the valve body 25 and is in contact with the outer peripheral surface of the large diameter portion of the valve body 25 and is close to the outer peripheral surface of the small diameter portion 25c with a gap.

According to the configuration of the present embodiment, the cylindrical holder 30 that covers the outer surface of the valve body 25 is installed at the valve body storage position of the valve chamber 24 when the valve is fully opened. Sometimes the valve body 25 is not directly exposed to the steam flow. Further, the valve body 25 is mechanically supported by the holder 30. Therefore, the support state of the valve body 25 is more stable than before,
Oscillation due to the fluid force of the steam flow is prevented. further,
By arranging the end of the holder 30 on the flow path side closer to the flow path side than the end of the valve body 25, it is possible to effectively prevent the contact with the steam flow particularly.

The outer peripheral surface of the intermediate portion of the valve body 25 has a small diameter portion 2 separated from the guide ribs 31a, 31b, 31c.
5c, the space around the valve body 25 is in a state of communicating in the circumferential direction, and unlike the conventional case, no closed space is formed around the valve body 25. Therefore, even if steam flows from the distal end of the holder 30 to the periphery of the valve body 25,
Are separated in the surrounding space, so that even if there is a difference in the fluid force of each steam flow, the difference is eliminated by the merge and becomes uniform, and the occurrence of vibration of the valve body 25 is prevented. Also, the guide ribs 31a, 31b, 31c are exposed inside the holder 30 and are arranged close to the outer peripheral surface of the small end of the valve body 25 with a gap therebetween, so that the holder 30 is temporarily provided.
Even if steam flows into the valve body 25 and the valve body 25 is exposed to the steam,
The difference between the fluid forces of the steam flows separated to the left and right of the valve body 25 is eliminated by the communication, and the vibration and the like of the valve body 25 are prevented.

FIGS. 3 and 4 show the specific operation and effect of this embodiment. In FIG. 3, the steam flows diverted to the left and right of the valve body 25 are denoted by a ′ and b ′, and the “force that vibrates the valve body” caused by the difference between these fluid forces is denoted by F. Then, the execution value of F is calculated for the present embodiment and the conventional example.
Each was examined.

As a result, as shown in FIG.
Assuming that the execution value of F is 1.0, the execution value of F in this embodiment is 0.25, which is confirmed to be reduced to about 1/4.

In the above-described embodiment, the configuration is provided with two elements, that is, the enclosing of the valve body 25 by the holder 30 and the communication in the circumferential direction of the surrounding space of the valve body 25. Even with a configuration having only one element, the occurrence of vibration can be prevented.

[0030]

As described above, according to the present invention, the valve body is directly placed by installing the cylindrical holder that covers the outer surface of the valve body at the valve body storage position when the valve is fully opened in the valve chamber. In addition, it is possible to prevent the valve body from being exposed to the steam flow, and the valve body is mechanically supported by the holder, whereby vibration of the valve body can be prevented. Further, by arranging the end of the holder on the flow path side closer to the flow path side than the end of the valve body, it is possible to particularly effectively prevent the contact with the steam flow.

[Brief description of the drawings]

FIG. 1 is an overall sectional view showing an embodiment of a main steam isolation valve of the present invention.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is a schematic view showing the operation of the present invention.

FIG. 4 is a table showing the operation of the present invention.

FIG. 5 is a schematic diagram showing a main steam system of a nuclear power plant.

FIG. 6 is an overall sectional view showing a conventional example of a main steam isolation valve.

FIG. 7 is a sectional view taken along line CC of FIG. 6;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 21 Primary flow path 22 Secondary flow path 23 Valve box 24 Valve room 25 Valve element 25a Tip part of valve element 25b Base end part of valve element 25c Small diameter part of valve element 28 Drive mechanism 30 Holder 31a, 31b, 31c Guide rib

──────────────────────────────────────────────────続 き Continuing on the front page (72) Katsumi Yamada 1 Toshiba-cho, Komukai-shi, Kawasaki-shi, Kanagawa Prefecture Toshiba Research Institute, Inc. (72) Noboru Saito 1 Toshiba-cho, Komukai-shi, Kawasaki-shi, Kanagawa Address Toshiba Research Institute, Inc. (72) Inventor Hideaki Takahashi 1 Tokoba, Komukai Toshiba-cho, Kawasaki-shi, Kanagawa Prefecture Toshiba Research Institute, Inc. (56) References JP-A-57-144356 (JP, A) 62-13548 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) F16K 1/00 F16K 1/32

Claims (2)

(57) [Claims] 1. A valve box having a cylindrical valve chamber which intersects at a fixed inclination between a primary flow path and a secondary flow path arranged substantially linearly, and is inserted into the valve chamber of the valve box in a piston shape. And a drive mechanism for driving the valve at a high speed, wherein a main steam isolation valve in which a portion from the middle part to the tip of the valve is disposed in the flow path when the valve is fully opened, At the valve body storage position of the valve chamber when the valve is fully opened, a cylindrical holder that covers the entire outer surface of the valve body is installed, and the lower end of the holder on the side of the flow path allows the fluid in the flow path to flow. A main steam isolation valve, wherein the main steam isolation valve is arranged closer to the closing drive direction side of the valve body in the flow path than the lower end portion of the valve body in the fully open position in the radial positional relationship of the vertical cross section with respect to the direction. . 2. The main steam isolation valve according to claim 1, wherein
The valve body is supported by a plurality of guide ribs on the outer periphery thereof in a valve chamber of the valve box, is inserted in a piston shape, is connected to a drive mechanism that drives at high speed, and has an outer peripheral surface of at least an intermediate portion of the valve body. It is a small diameter portion that is smaller in diameter than the outer peripheral surface of the pipe side end of the valve body and is isolated from the guide ribs, whereby the space around the valve body communicates in the circumferential direction, and furthermore, each of the guide ribs is located inside the holder. A main steam isolation valve, wherein the main steam isolation valve is exposed so as to be close to the outer peripheral surface of the small diameter portion of the valve body with a gap.